Method for Decoding Data in Non-Volatile Storage Using Reliability Metrics Based on Multiple Reads

1. A method for decoding data in non-volatile storage, comprising: performing multiple sense operations, including a first sense operation and at least one subsequent sense operation, on at least one non-volatile storage element; and determining a programming state of the at least one non-volatile storage element using iterative probabilistic decoding, the iterative probabilistic decoding uses reliability metrics which are based on the multiple sense operations, wherein the iterative probabilistic decoding iterates initially using first reliability metrics which are based on the first sense operation but not the at least one subsequent sense operation, the first reliability metrics are adjusted to obtain adjusted reliability metrics as the iterative probabilistic decoding iterates, and the adjusted reliability metrics are adjusted, as the iterative probabilistic decoding iterates further, based on the at least one subsequent sense operation.

2. The method of claim 1 , wherein the reliability metrics comprise logarithmic likelihood ratios.

3. The method of claim 1 , further comprising: for each of the multiple sense operations, providing bits which represent a sensed programming state of the at least one non-volatile storage element, the reliability metrics are provided for each of the bits.

4. The method of claim 3 , further comprising: reading a table which cross references sensed programming states and bits to reliability metrics.

5. The method of claim 1 , wherein the iterative probabilistic decoding attempts to satisfy parity checks of an error correction code.

6. The method of claim 1 wherein the adjusted reliability metrics are adjusted to indicate a higher reliability when a sensed programming state of the at least one subsequent sense operation is consistent with a sensed programming state of the first sense operation.

7. The method of claim 1 , further comprising: restarting the iterative decoding process using probability metrics which are based on the first sense operation and the at least one subsequent sense operation.

8. The method of claim 1 , further comprising: obtaining voltage threshold profiles of the at least one non-volatile storage element for each of a plurality of programming states based on a plurality of sense operations performed on a set of non-volatile storage elements; providing a set of reliability metrics based on the voltage threshold profiles; and accessing the reliability metrics which are used in the iterative probabilistic decoding from the set of reliability metrics.

9. The method of claim 8 , wherein the providing the set of reliability metrics comprises: determining a conditional probability function f1(u|X) based on the plurality of sense operations, where u indicates a sensed threshold voltage and X represents a programmed state of the plurality of programming states; and determining a probability function f2(v) based on the plurality of sense operations, for each programming state, where v indicates a deviation of a sensed threshold voltage from a threshold voltage free of read noise.

10. The method of claim 9 , wherein the providing the set of reliability metrics further comprises: determining logarithmic likelihood ratios based on the conditional probability function f1(u|X) and the probability function f2(v).

11. A non-volatile storage system, comprising: a set of non-volatile storage elements; and one or more control circuits in communication with the set of non-volatile storage elements, the one or more control circuits perform multiple sense operations, including a first sense operation and at least one subsequent sense operation, on at least one non-volatile storage element of the set and determine a programming state of the at least one non-volatile storage element using iterative probabilistic decoding, the iterative probabilistic decoding uses reliability metrics which are based on the multiple sense operations, wherein the iterative probabilistic decoding iterates initially using first reliability metrics which are based on the first sense operation but not the at least one subsequent sense operation, the first reliability metrics are adjusted to obtain adjusted reliability metrics as the iterative probabilistic decoding iterates, and the adjusted reliability metrics are adjusted, as the iterative probabilistic decoding iterates further, based on the at least one subsequent sense operation.

12. The non-volatile storage system of claim 11 , wherein the reliability metrics comprise logarithmic likelihood ratios.

13. The non-volatile storage system of claim 11 , wherein for each of the multiple sense operations, the one or more control circuits provide bits which represent a sensed programming state of the at least one non-volatile storage element, the reliability metrics are provided for each of the bits.

14. The non-volatile storage system of claim 13 , wherein the one or more control circuits read a table which cross references sensed programming states and bits to reliability metrics.

15. The non-volatile storage system of claim 11 , wherein the iterative probabilistic decoding attempts to satisfy parity checks of an error correction code.

16. The non-volatile storage system of claim 11 , wherein the one or more control circuits adjusts the adjusted reliability metrics to indicate a higher reliability when a sensed programming state of the at least one subsequent sense operation is consistent with a sensed programming state of the first sense operation.

17. The non-volatile storage system of claim 11 , wherein the one or more control circuits restarts the iterative decoding process using probability metrics which are based on the first sense operation and the at least one subsequent sense operation.

18. The non-volatile storage system of claim 11 , wherein the one or more control circuits obtain voltage threshold profiles of the at least one non-volatile storage element for each of a plurality of programming states based on a plurality of sense operations performed on a set of non-volatile storage elements, provide a set of reliability metrics based on the voltage threshold profiles, and access the reliability metrics which are used in the iterative probabilistic decoding from the set of reliability metrics.

19. The non-volatile storage system of claim 18 , wherein the one or more control circuits provide the set of reliability metrics by determining a conditional probability function f1(u|X) based on the plurality of sense operations, where u indicates a sensed threshold voltage and X represents a programmed state of the plurality of programming states, and determining a probability function f2(v) based on the plurality of sense operations, for each programming state, where v indicates a deviation of a sensed threshold voltage from a threshold voltage free of read noise.

20. The non-volatile storage system of claim 19 , wherein the one or more control circuits provide the set of reliability metrics by determining logarithmic likelihood ratios based on the conditional probability function f1(u|X) and the probability function f2(v).

21. A method for decoding data in non-volatile storage, comprising: performing a first sense operation and at least one subsequent sense operation on at least one non-volatile storage element; performing iterative probabilistic decoding including iterating using first reliability metrics which are based on the first sense operation but not the at least one subsequent sense operation, adjusting the iterative probabilistic decoding and the first reliability metrics to obtain adjusted reliability metrics as the iterative probabilistic decoding iterates, and adjusting the adjusted reliability metrics, as the iterative probabilistic decoding iterates further, based on the at least one subsequent sense operation; and determining a programming state of the at least one non-volatile storage element based on the iterative probabilistic decoding.